The goals of the Animal Facility Core are to provide well-defined SAMR1, SAMP6 and IL-6 knockout mice for the investigators of the program project, and to assist investigators in the design and conduct of animal studies. This Core will be a cost-effective means of properly maintaining precious breeding stocks of mice that are essential for the conduct of experiments proposed by investigators in the program project. Economy will also be served by pooling requests for animals to be used in experiments. The Core will also be a centralized source for information on individual mice maintained by the facility. To achieve these goals the Animal Facility Core will perform the following. 1. Maintain a database on mice in the colon. Each animal will be electronically tagged at weaning. Information such as the date of birth, weight at weaning, identity of parents, and other features obtained by measurement or observation, will be recorded in a computerized database. This information will be available to each investigator and will be used by the Core Leader, in conjunction with project leaders, to select animals for experiments. 2. Maintain inbred mouse strains and assess genotype of each strain. Foundation stocks of SAMR1, SAMP6 and IL-6 knockout mice will be established; and production colonies of each strain will be set up as needed to produce animals for the conduct of experiments by investigators in the program project. For each colony, the Core will select breeders to minimize strain divergence. To assure strain authenticity, the genotype of SAMR1 and SAMP6 mice will be monitored by determining the H-2K haplotype, or by analysis of sequence length polymorphic microsatellite markers that uniquely identify the genome of each strain. In the case of the IL-6 knockout colony, genotype will be assessed by detection of the truncated IL-6 gene by Southern blotting. In conjunction with Jackson Laboratories (Bar Harbor, ME) embryos of the SAMP6 and SAMR1 mouse strains will be cryogenically preserved so that each strain can be reconstituted in case the breeding stock is lost. Finally, the overall health of each colony will be assessed periodically by necropsy. 3. Assist in conduct of animal experiments. Animal Facility Core personnel will conduct routine procedures in coordination with personnel in the Division of Laboratory Animal Medicine of UAMS. These include surgical procedures, administration of reagents or experimental test materials to mice, preparation of anesthetized animals for determination of bone mineral density by dual energy X-ray absorptiometry, and collection of serum and urine samples.